PCI/MSI: Let core code free MSI descriptors

Set the domain info flag which tells the core code to free the MSI
descriptors from msi_domain_free_irqs() and add an explicit call to the
core function into the legacy code.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Bjorn Helgaas <bhelgaas@google.com>
Link: https://lore.kernel.org/r/20211206210748.089085131@linutronix.de